Signs
The signage used is the standard European one.
A notable difference from France: motorways are indicated by GREEN signs, main roads by BLUE signs.
Roads are classified as Ax (Autostrade, x: number) SS (Strada Statale), SR (Strada Regionale), SP (Strada Provinciale); roughly corresponding to French national, regional and departmental roads.
The further south you go in Italy, the rarer the directions become outside the main roads, and they even seem sometimes irrational. A map or a GPS often proves indispensable. 
A particular sign often marks the entrance to city centres where traffic is restricted and subject to conditions: see ZTL traffic in Italian cities.
Motorways
The motorways are marked by GREEN signs, named for example “A1”.
The network is very good north of Naples, most are tolled, but are cheaper than in France. The Sicilian network, recent, is also of good quality.
Note on motorway indications : either they designate a direction (like NAPOLI A1), or they designate a motorway such as: BARI-NAPOLI A4, to show the direction of the motorway linking BARI to NAPOLI (and therefore not directly the direction towards BARI or NAPOLI)
South of Naples, in Campania and Calabria in particular, the motorways are mostly free but often poorly maintained, although the motorway linking Naples to Sicily via Reggio is being rehabilitated.
The presence of potholes is not surprising, care should be taken, as speed limits often correspond to a deterioration of the road surface.
Behaviour
Neither the horn nor headlight flashes are considered aggressive.
A headlight flash from a vehicle behind on the motorway is a way of indicating its presence to the vehicle ahead with the intention of overtaking. Drivers’ speeds are sometimes excessive.
